The present invention relates to a book block clamp for clamping and transporting book blocks in book block processing machines.
Book block processing machines have a transport system which comprises a multitude of book block clamps that are continuously movable in a closed circulation path and that are arranged at equal mutual spacing from each other. Such book block clamps move in a guideway and are connected to a transport chain that provides the driving force. The outer clamping jaw of the book block clamps can be slid horizontally and at a right angle to the direction of movement of the book block clamp, wherein the book block clamps are controllable between a closed position for clamping, and an open position for infeed or delivery of the book block.
A book block clamp of this type is for example shown in DE-OS 21 10 836. At the ends of its outer clamping jaw the book block clamp comprises toothed racks that are slidable along the longitudinal axis in the inner clamping jaw, and which engage pinions on the end of an arbor which is held in the inner clamping jaw so as to be parallel to the outer clamping jaw. Behind the inner clamping jaw the two toothed racks are brought together by a bar which causes the movement for opening and closing by running on a cam roller. By way of a torsion spring that is seated on the parallel arbor, wherein one end of the torsion spring is connected to the inner clamping jaw, the clamping force required for holding the book block is generated. Starting with pretensioning, the torsion spring tensions as the distance between the clamping jaws increases, and consequently an effective clamping force of the book block clamp is generated depending on the block thickness. It is not possible to exert a defined clamping force that is independent of the block thickness. Finally, to hold the open position of the clamping device, a reverse drive lock in the form of a further coil spring arranged on the arbor is provided.
DE 32 07 102 C2 discloses another book block clamp which provides for clamping jaws that are guided in parallel. Its outer clamping jaw is guided so as to be freely slidable on a guide rod by way of a slide guide, wherein the guide rod is located on one side of the inner clamping jaw. The outer clamping jaw itself comprises a clamping plate, which is accommodated by the slide guide by means of a parallel control arm arrangement. Between the parallel control arm arrangement and the clamping plate there is a compression spring which exerts a clamping force on the book block, wherein the clamping force of increases with increasing spring action from a defined pretensioning force to the maximum force. The contact pressure on the outer clamping jaw that is freely slidable on the guide is exerted by a closing cam that is installed on the side of the movement path of the circulating book block clamp, wherein a cam roller of the slide guide of the outer clamping jaw contacts the closing cam. The distance between the closing cam and the inner clamping jaw can be set in accordance with the book block thickness or the desired clamping force to be exerted. In order to maintain the clamping force exerted on the book block by the closing cam and the compression spring when the book block clamp leaves the region of the closing cam, the slide guide comprises a self-locking cam locking mechanism which when an outward-acting force is experienced locks the outer clamping jaw.
In known book block processing machines comprising parallel-closing book block clamps the respective book block, positioned on its spine, is fed to the opened book block clamp diagonally from below. In this arrangement, the book block is advanced by a pusher of a transport chain right up to a horizontal tabletop, while it is laterally guided by the inner and outer clamping jaws of the book block clamp. Finally the book block is aligned by resting its rear edge against a book stop catch of the book block clamp and is then clamped by the book block clamp.
For functionally secure lateral guidance of unbound book blocks comprising a multitude of layers and/or single sheets, the opening stroke of the book block clamp is to be limited to a minimum. However, due to fixed cam geometries for controlling the opening and/or closing movement, only a maximum opening stroke is provided, which is designed for a book block with voluminous paper and maximum block thickness. To reduce the opening stroke, only part of the stroke of the respective cam is used, wherein the cam roller encounters a rising cam flank, thus producing a corresponding jerk or jolt in the opening- and/or closing movement. Book block processing machines are known in which the book block clamps are always operated with the full cam stroke, wherein the cam roller contacts the cam without jerking or jolting. However, the resulting opening width in the case of thin book blocks is too wide to provide reliable guidance during infeed to the book block clamp, in particular when unstable layers and/or single sheets of an unbound book block are involved.